To satisfy demands for wireless data traffic, which have been increasing since commercialization of a 4th generation (4G) communication system, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. That is why the 5G or pre-5G communication system is referred to as a beyond 4G network communication system or a post long term evolution (LTE) system. To achieve high data rates, deployment of the 5G communication system in a millimeter wave (mmWave) band (i.e., a 60-GHz band) is under consideration. In order to mitigate propagation path loss and increase a propagation distance in the mmWave band, beamforming, massive multiple input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna technology have been discussed for use in the 5G communication system. Further, to improve a system network, techniques such as an evolved small cell, an advanced small cell, a cloud radio access network (cloud RAN), an ultra-dense network, device-to-device (D2D) communication, a wireless backhaul, a moving network, cooperative communication, a coordinated multi-point (CoMP), and an interference cancellation have been developed for the 5G communication system. Besides, advanced coding modulation (ACM) techniques such as hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC), and advanced access techniques such as filter bank multi carrier (FBMC) and non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed for the 5G communication system.
The Internet is evolving from a human-oriented connection network in which human beings generate and consume information to the Internet of things (IoT) in which information is transmitted/received and processed between distributed elements such as things. The Internet of everything (IoE) technology is emerging, which combines the IoT with big data processing through connectivity to a cloud server and the like. For IoT implementation, technologies such as sensing, wired/wireless communication and network infrastructure, service interfacing, and security are required. Currently, techniques including a sensor network for interconnection between things, machine to machine (M2M) communication, and machine type communication (MTC) are being studied. An intelligent Internet technology (IT) service of creating new values for human beings by collecting and analyzing data generated from interconnected things may be provided in an IoT environment. The IoT may find IoT applications in a wide range of fields including a smart home, a smart building, a smart city, a smart car or a connected car, a smart grid, health care, a smart appliance, and a state-of-the art medical service, through convergence between existing IT technologies and various industries.
In this context, many attempts have been made to apply the 5G communication system to the IoT. For example, techniques such as a sensor network, M2M communication, and MTC are implemented by means of beamforming, MIMO, array antennas, and the like for 5G communication. Application of cloud RAN as the afore-described big data processing technique is an example of convergence between 5G technology and IoT technology.
To process the recently ever-increasing mobile data traffic, the 5G system after the LTE (or an evolved universal mobile telecommunications system (UMTS) terrestrial radio access (E-UTRA)) and LTE-advanced (LTE-A) (or E-UTRA Evolution) systems is under active discussion. While a system bandwidth per carrier is limited to up to 20 MHz in the legacy LTE and LTE-A systems, the 5G system seeks to provide ultra-high-rate data service at up to a few Gbps in an ultra-wide band much wider than in the legacy LTE and LTE-A systems. Since it is difficult to secure the ultra-wide band frequency in a frequency band spanning hundreds of MHz to a few GHz, an ultra-high frequency band of a few GHz or tens of GHz is considered as a candidate operating frequency band for the 5G system.
Waves in the ultra-high frequency band have a wavelength of a few mm and thus are called an mmWave. In the ultra-high-frequency band, however, the pathloss of waves increases in proportion to a frequency band, resulting in the coverage of a mobile communication system.
To overcome the shortcoming of reduced coverage, beamforming is emerging as important because the beamforming increases the propagation distance of waves by focusing the radiation energy of waves onto a predetermined target spot through a plurality of antennas. Beamforming is applicable to each of a transmitter and a receiver. In addition to coverage extension, beamforming offers the benefit of interference mitigation in areas other than a beamforming direction. To implement beamforming appropriately, accurate measurement of a transmission/reception beam and a feedback method are needed.
Another requirement for the 5G system is ultra-low latency service with a transmission delay of more or less 1 ms. As a method for reducing a transmission latency, a short transmission time interval (TTI)-based frame structure needs to be designed, compared to a frame structure in the LTE and LTE-A systems. A TTI is a basic scheduling unit. In the legacy LTE and LTE-A systems, a TTI is 1 ms, the length of one subframe. For example, 0.5 ms, 0.2 ms, 0.1 ms, and the like is available as a shorter TTI than in the LTE and LTE-A systems to satisfy the requirement of the ultra-low latency service in the 5G system. Unless otherwise mentioned, the terms TTI and subframe are interchangeably used in the sense that they represent a predetermined time interval as a basic scheduling unit.
Now, the LTE and LTE-A systems will be described with reference to the attached drawings, and a design sought for the 5G system will also be described.
FIG. 1 illustrates a basic structure of a radio resource area, that is, a time-frequency resource area, which carries data or a control channel in the legacy LTE and LTE-A systems according to the related art.
Referring to FIG. 1, a horizontal axis represents time, and a vertical axis represents frequency.
Uplink (UL) refers to a radio link through which a user equipment (UE) transmits data or a control signal to an evolved node B (eNB), and downlink (DL) refers to a radio link through which an eNB transmits data or a control signal to a UE. In the LTE and LTE-A systems, a minimum time unit is an orthogonal frequency division multiplexing (OFDM) symbol on DL and a single carrier frequency division multiple access (SC-FDMA) symbol on UL. One slot 106 includes Nsymb symbols 102, and one subframe 105 includes two slots. A slot is 0.5 ms long, and a subframe is 1.0 ms long. A radio frame 114 is a time unit including 10 subframes. A minimum frequency unit is a subcarrier of 15 kHz, and a total system transmission bandwidth covers NBW subcarriers 104.
A basic resource unit in the time-frequency domain is a resource element (RE) 112, represented by an OFDM symbol or SC-FDMA symbol index and a subcarrier index. A resource block (RB) or physical RB (PRB) 108 is defined by Nsymbol consecutive OFDM symbols 102 in time by NRB consecutive subcarriers 110 in frequency. Therefore, one RB 108 includes Nsymb×NRB REs 112. In the LTE and LTE-A systems, data is mapped in units of an RB, and an eNB schedules a specific UE in units of an RB pair included in one subframe. The number of SC-FDMA or OFDM symbols, Nsymb is determined according to the length of a cyclic prefix (CP) added to each symbol in order to prevent interference. For example, Nsymb is 7 in the case of a normal CP, and Nsymb is 6 in the case of an extended CP. NBW and NRB are proportional to a system transmission bandwidth. A data rate increases for a UE in proportion to the number of RBs scheduled for the UE.
FIG. 2 illustrates a method for mapping a control channel and a data channel to a time-frequency resource area as defined above in the LTE and LTE-A systems according to the related art.
Referring to FIG. 2, the horizontal axis represents time and the vertical axis represents frequency. In the LTE and LTE-A systems, a basic scheduling unit is a subframe 201. In general, an eNB determines whether to schedule a UE in each subframe and transmits on a data channel and a control channel carrying scheduling information about the data channel to the UE according to the determination. The control channel is generally mapped to the first one to three OFDM symbols of a subframe in time and to a total system bandwidth 202 in frequency, as indicated by reference numeral 203. Therefore, the UE may complete processing of the control channel as early as possible, and frequency diversity may be maximized. As a consequence, the reception performance of the control channel is increased. The data channel scheduled by the control channel is mapped to the symbol following the last symbol of the control channel to the last symbol of the subframe in time and to a range within the system bandwidth in frequency according to the scheduling determination of the eNB, as indicated by reference numeral 204. Accordingly, the UE should be capable of always receiving a signal across the total system bandwidth irrespective of the size of a frequency area occupied by an actually scheduled data channel. Although it does not matter with UE implementation in the LTE or LTE-A system having a relatively narrow system bandwidth 202, the complexity of UE implementation may increase excessively in the 5G system with an ultra-wide system bandwidth 202. For example, UEs supporting only a partial bandwidth (a subband 205) within a 5G system bandwidth which does not increase complexity relatively may be introduced in the early deployment stage of the 5G system in order to proliferate 5G UEs as fast as possible. If a 5G control channel is distributed across the system bandwidth as in the legacy LTE and LTE-A systems, the 5G UEs supporting only the subband cannot receive the 5G control channel.
As a result, the 5G UEs supporting only the subband cannot use the radio resources of an area 206, which is inefficient. Likewise, if a channel occupying the total system bandwidth is defined as in the legacy LTE and LTE-A system, limitations may be imposed on efficient resource use of future-introduced various 5G services. That is, forward compatibility is limited.
FIG. 3 illustrates a hybrid automatic repeat request (HARQ) feedback timing in a legacy LTE and LTE-A systems according to the related art.
Referring to FIG. 3, LTE and LTE-A systems may support frequency division duplex (FDD) and time division duplex (TDD).
Different frequencies are used for DL and UL in FDD, whereas a common frequency is used for DL and UL and a UL signal and a DL signal are distinguished from each other in time in TDD.
In TDD, a DL signal or a UL signal is transmitted separately on a subframe basis. Accordingly, various TDD UL-DL configurations are defined so that a time area may be divided equally into UL and DL subframes, more DL subframes may be allocated, or more UL subframes are allocated, according to traffic loads.
In an FDD LTE or LTE-A system, if an eNB transmits a data channel and a related control channel in subframe #n 301 to a UE, the UE transmits an HARQ acknowledgment/negative acknowledgment (ACK/NACK) feedback indicating whether the data channel has been received successfully in subframe #n+4 302 to the eNB.
On the other hand, in a TDD LTE or LTE-A system, an HARQ ACK/NACK feedback timing corresponding to each subframe is defined for each TDD UL-DL configuration.
HARQ ACK/NACK feedback timings may additionally be defined according to support or non-support of carrier aggregation (CA) and combinations. In other words, implementation complexity may be increased due to various HARQ ACK/NACK feedback timings.
Further, an eNB transmits DL data and scheduling information to UEs. In a general wireless communication system, information about an outband signal carrying control information mapped to radio resources separately from data in each subframe should be acquired. Consequently, overhead is increased.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.